Before purchasing paints, buyers typically are given a fan deck or palette comprising hundreds or thousands of paint chips, which represent a small portion of the available paint colors. The paint chips can be created by variety of means including inkjet printing. The paint chips typically measure about 1¼ inch by 2 inches, and recently, buyers can purchase larger paint chips of about 18 inches by 18 inches to assist them with the mental projection of the colors to the walls. Additionally, the buyers may purchase small containers of about 2 ounces of the desired paints to paint larger swatches on the walls. Typically, the buyers start with small paint chips to narrow the choices and then move to larger paint chips and/or sample paints before choosing the final paint colors.
Color accurate, physical merchandise, which has a tactile dimension as well as color, is available in a nearly unlimited variety of shapes and sizes. These include the basic, single color chips described above, as well as strip chips, fan decks, designer decks, counter books, specialty collections and variations of all of these. The merchandise may be used by consumers or design professionals and may appear in retail stores, kiosks, design centers or be available for sale through stores or via the internet. All of this physical color merchandise is produced through an industrial process that requires quite large production runs to achieve economies of scale. Consequently, there are long lead times and relatively high inventory levels. Once produced, there is little flexibility to revise the form factor, by re-cutting and re-collating for instance. The color control of this physical merchandise is generally very good, including the control of metamerism which is managed by using pigment combinations that match as closely as possible the final product, in this case decorative paints. However, this type of merchandise cannot provide immediately available, customized or short run color merchandise. Onsite printing of color merchandise can meet this need. However, print technology has not yet been adequately accurate to meet the required quality standard. Specifically, the ability to produce non-metameric (or minimally metameric) color merchandise is not yet achievable.
Recently, paint viewing or paint selection software, such as Benjamin Moore® Paints' Personal Color Viewer™ (“PCV”) available either on the World Wide Web or as CD-ROM, has improved the paint selection process for buyers. The PCV software displays on a computer screen a number of standard interior rooms with furniture, e.g., living room, dining room, bedrooms kitchen and bathroom, as well as the exteriors of a dwelling. The buyers can change the colors of the room, including ceiling, trim and upper and lower walls, at will to project the colors to the entire room. Additionally, digital images of the buyers' own dwellings can be manipulated by the PCV software to display the desired colors.
However, many conventional paint selection tools, e.g., paint chips and paint selection software, are subject to the effects of color inconstancy and metamerism. It is known that colors can look different under different viewing conditions. Thus, a consumer may observe that a particular color, or a pair of colors, has one appearance under one ambient light or illuminant but has a different appearance under a different ambient light or illuminant.
Color inconstancy is the change in color perception of a single physical color under different light sources. Light sources are often identified by two important parameters: color temperature (CT) and spectral power distribution. The CT of a light source is determined by comparing its chromaticity with that of an ideal blackbody radiator. When the given light source has the same CIE 1931 chromaticity co-ordinates as that of a blackbody radiator (Planckian radiator) at a certain temperature (in Kelvin units), this temperature is called the color temperature of the light source. For example, CIE Illuminant A has a CT of 2856K. On the other hand, the term correlated color temperature (CCT) is introduced when the chromaticity of a given light source is not exactly equal to any of the chromaticities of a black body radiator. The CCT is defined as the temperature of the blackbody radiator whose perceived color most closely resembles that of the given light source at the same brightness and under specified viewing conditions. For example, some fluorescent daylight lamps have a CCT of 6500K.
The spectral power distribution, SPD, is a measure of the amount of energy emitted by the light source at each wavelength in the visible spectrum. This information is usually reported at 1, 2, 5, 10 or 20 nanometer intervals. For example, a color observed outdoors is illuminated by the sun with a wide range of CCT and SPD from sunrise to sunset. Indoor illumination or artificial light is rarely as bright as natural sunlight and differs considerably in SPD and may also differ in CCT. Illumination is an important factor in viewing colors, and the brightness of the environment, as well as the CCT and SPD, have a measurable effect on colors perceived by people. This effect explains why a consumer sometimes thinks that a sample paint color, such as the color of a paint chip, appears different at home (e.g., under incandescent light) than the way that paint color had appeared at a retail store (e.g., under fluorescent light). Some colors shift more than others under different light sources; colors that shift to a greater degree are said to have a higher degree of inconstancy.
Another drawback of paint chips, paint selection software, and other conventional color selection tools is that they are subject to metamerism. Two or more colors may have the same color appearance under one ambient lighting condition, but may appear to be different colors under another ambient lighting condition. This is caused by the color pigment combinations of the paints being different from each other resulting in different spectral reflectance factors (SRF), which is a measure of the amount of energy reflected from a sample object at the wavelengths of visible light. Typically these are reported at 1, 2, 5, 10 or 20 nanometer intervals. As an example, consider a green paint chip side-by-side with an actual green paint applied on a wall. Since this paint chip is made with certain pigment combinations and the paint is made with different pigments, their chemical and pigment compositions are different and would reflect light differently. Hence, while both may appear the same color under one light source, they may appear as different colors or non-matching colors, or different shades of the same color, under a different light source. More particularly, in natural daylight, both the paint chip and painted wall appear to be the same shade of green. However, when viewed under incandescent light, while the paint on the wall may still appear green, the paint chip color could appear as a different shade of green. Accordingly, consumers appreciate the need for paint selection tools that exhibit minimal metamerism in reference to colors or paints.
The patent and scientific literatures disclose a number of attempts to address the problem of metamerism. U.S. Pat. No. 6,259,430 B1 discloses a method of displaying colors that allegedly can control the metameric effect. This method divides the radiation spectrum into at least four wavelength bands and selects a single representative wavelength in each band. The intensity of each representative wavelength is selected, and a plurality of radiation beams at the selected intensities and representative wavelengths are generated and combined to produce the desired color.
U.S. Pat. No. 7,053,910 B2 discloses a method for reducing metamerism in color management systems. This method applies multiple different inverse transforms to a color value in perceptual color space, one each for multiple different viewing conditions, thereby resulting in plural different target color values in a viewing condition dependent space. Subsequently, a single color value in destination device dependent color space is obtained through best-fit regression analysis (e.g., weighted regression analysis), thereby minimizing metameric shifts in color appearance due to changes in viewing conditions.
Inkjet printers use dye-based inks and pigment-based to print on papers. Dye-based inks can mix as they are being printed and are absorbed into the papers leaving very little ink on the surface of the papers. Dye-based inks can provide a large color gamut, but are susceptible to color fading. A number of inkjet manufacturers have produced pigment-based inks in order to address the color fading issue, and pigment-based inks are durable. Pigment-based inks comprise solid color pigments suspended in resin similar to architectural coatings and paints, and the solid color pigments, which can be organic and/or inorganic, are not absorbed into the papers, but are deposited on top of the papers and held to the papers by the resin.
However, there still remains a need in the art for an improved method of managing metamerism, especially of printed color merchandise, which can assist consumers in selecting paint colors.